In particular with his macho-man image, getting ill is bad, getting ill from a virus he his downplayed is even worse. Hence the posturing as not that ill. Which in turn works poorly when he has to go to the hospital and is quite clearly ill.

A politician with a more humble image might get a sympathy vote from getting ill. Norwegian PM Bondevik had a depressive period and on sick leave while being PM in late 90ies and if anything it appears to have strenghtened him politically.